The present invention relates to an adaptive postprocessing system for reducing blocking effects and ringing noise of an image signal. More particularly, the system of the present invention adaptively attenuates blocking effects and ringing noise appearing in a decompressed image which has been subject to highly efficient image compression.
Most picture coding standards, including H.263 of the International Telecommunication Union (ITU) and MPEG-1 and MPEG-2 of the Organization for Standardization (ISO), use block-based processing for motion estimation and discrete cosine transformation (DCT). It is well-known that such block-based processing induces blocking effects and the ringing noise, which is particularly noticeable when an image has been highly compressed. Typical blocking effects include grid noise in monotone areas and the staircase noise along the image edges. Due to these effects, a viewer who views the decompressed image displayed on a screen perceives the boundary between the blocks composing the decompressed image. The ringing noise produces sinusoidal traces on the edges of an image.